1. Field of the Invention
The present invention relates generally to the production of semiconductor products. More particularly, the invention relates to a method of filling trenches, holes and other surface discontinuities in semiconductor products. The invention also relates to an apparatus for forcing conductive metal into openings in semiconductor products.
2. Discussion of the Related Art
A method of filling metal into openings in semiconductor products is described in U.S. Pat. No. 5,527,561 (Dobson). According to the Dobson process, via holes are formed in a semiconductor wafer. An aluminum layer is formed over the holes by sputtering. The aluminum layer is deformed and caused to flow into the holes by high pressure and high temperature. The high pressure is applied by pressurized gas.
The Dobson process has several disadvantages. First, it may not always fill the via holes as desired. The process will not work unless the holes are completely covered over by aluminum. That is, the process will not work if openings in the aluminum layer permit equalization of the pressures inside and outside the holes. Openings in the aluminum layer may be formed during the sputtering process or during the application of high pressure and high temperature.
Another problem with the Dobson process is that it would be difficult to operate efficiently. It takes time to pressurize the gas in the Dobson process. The time it takes to handle the pressurized gas reduces the rate at which wafers can be processed. In addition, the mechanisms that would be used to create and maintain the high pressure are relatively large and complicated.
The disadvantages of the prior art are overcome to a great extent by the present invention. The invention uses explosive force to fill trenches, via holes and/or other openings or surface discontinuities.
The invention relates to a method of making a semiconductor product. The method includes the steps of providing a conductive layer on an insulating layer, and applying an explosive force to the conductive layer. The explosive force is used to efficiently and reliably drive the conductive material into openings defined in the insulating layer.
According to one aspect of the invention, the conductive material is a malleable metal material. The semiconductor product may be a semiconductor wafer in an intermediate stage of production. The metal material may form electrical interconnects in the wafer.
The explosive force may be provided by a variety of reactive materials and other instrumentalities. In one embodiment of the invention, the explosive force is generated by igniting a mixture of hydrogen and oxygen. In another embodiment of the invention, the reactive materials include alcohol and a suitable oxidizing agent.
To control or buffer the explosive force, a baffle may be interposed between the explosion and the wafer being processed. The baffle may be a solid structure. Alternatively, the wafer may be immersed in liquid or gas. In another embodiment of the invention, a piston is used to transmit and/or regulate the explosive force.
According to another aspect of the invention, the conductive material is softened by preheating, before the explosive force is applied to it.
The present invention also relates to an apparatus for processing semiconductor wafers. The apparatus includes a support member for supporting the wafers and a reaction chamber for containing explosive forces. In a preferred embodiment of the invention, the apparatus also includes a heater for preheating the wafers. In addition, an ignition device may be provided for initiating combustion reactions.
An advantage of the invention is that it may be practiced with compact equipment. The invention does not require bulky, complicated mechanical systems for producing and handling pressurized gas.
Another advantage of the invention is that explosive forces can be generated consistently and rapidly, resulting in faster sequential processing of semiconductor wafers.
Moreover, it has been found that explosive forces, characterized by high energy waves, are preferable to forces produced by gradually increasing gas pressure, in terms of reliably forming high quality electrical interconnects.
The present invention is particularly well suited for filling trenches and holes that have high height to width aspect ratios.
According to one aspect of the invention, a porous baffle may be used to protect semiconductor wafers from contaminants, such as contaminants created by sliding pistons. The baffle may be formed, for example, of sintered stainless steel.
According to another aspect of the invention, a piston with differential surface areas may be used to increase or decrease the intensity of waves applied to the surfaces of the wafers being processed. If desired, an annular space at the periphery of the piston may be maintained at atmospheric pressure to further protect the wafers from contaminants.
An advantage of the present invention is that it can be practiced with both gaseous and liquid fuels and oxidizing materials. According to one aspect of the invention, the oxidizer may be supplied to the reaction chamber under relatively high pressure.
These and other features and advantages of the invention will become apparent from the following detailed description of preferred embodiments of the invention.